As of March 2010[update], the largest known (real) Eisenstein prime is 19249 × 213018586 + 1, which is the tenth largest known prime, discovered by Konstantin Agafonov.[1] All larger known primes are Mersenne primes, discovered by GIMPS. Real Eisenstein primes are congruent to 2 mod 3, and Mersenne primes (except the smallest, 3) are congruent to 1 mod 3; thus no Mersenne prime is an Eisenstein prime.